The present invention describes a specific application of the temperature sensor, without thereby being limited to same. The application relates to the rail transport sector and in particular to the reading and related monitoring of the temperature in the vicinity of a roller bearing of an axle of a railway vehicle.
Although particularly suited to railway use, the present invention is nonetheless applicable to any other related technical sector, such as (but without limitation) the industrial sector or the off-highway sector. In all of the applications mentioned, the invention can be used both if the inner ring of the bearing is rotatable while the outer ring of the bearing is fixed, or vice versa. Furthermore, the invention can be used regardless of the rolling members used (spheres, rollers, conical rollers, etc.).
In the railway vehicle sector, roller bearings for the axles of railway vehicles are subject to high stresses. In particular, the bearings used on railway axles are usually found in pairs and are interposed between the suspension and the flanged wheel of the vehicle. The bearing is seated in a housing, or “axle box”, and the stress transmitted by the suspension creates a significant temperature increase during operation. This temperature must be monitored at all times, since an over-temperature reading indicates a malfunction of the system. Specifically, three alarm thresholds are used:
A first alarm threshold is reached when a predetermined absolute temperature value is exceeded,
A second alarm threshold is reached when the difference between the temperature of the bearing and the temperature of the external environment exceeds another predetermined value,
Finally, a third alarm threshold is reached when a predetermined temperature difference between the two bearings of a single railway axle is exceeded.
This requirement reveals a clear need to constantly monitor the temperature of the bearing to determine the temperature at a point close to the most stressed zone of the bearing.
The temperature is monitored using a temperature sensor for each bearing that is connected electrically to a control unit that uses the temperature values read by the censors to manage activation of the alarms related to the aforementioned temperature thresholds being exceeded.
The temperature sensor is provided with a temperature-sensitive element that is inserted in the housing containing the bearing and reads the temperature of the housing close to the point of the bearing subject to the greatest stress.
The sensor needs to be stably attached to the housing, the electrical cable of same must not rotate during assembly, and same must be properly sealed. Failure to satisfy these conditions has an obvious adverse effect on the transmission of temperature signals.
Satisfying these requirements complicates assembly of the temperature sensor, requiring observance of very precise tolerances, and in any case a somewhat long and laborious assembly process. In particular, there are two known solutions to ensure that the temperature sensor is in stable contact with the surface from which the temperature reading is to be taken:
A first solution involves providing the sensor with a protrusion of very specific diameter and—in particular—length, and providing the housing with a hole of equally precise dimensions, such as to guarantee a good connection with the protrusion of the sensor. The sensor may be attached to the housing by means of a suitable flange and attachment screws. This means that the housing is designed to have at least three holes, one of which is very precise.
To avoid such stringent machining tolerances, a second known solution involves screwing the sensor into the hole in the housing. In this way, both components can be provided with a thread without restrictive tolerances. However, the drawback of this solution is linked to the fact that the cable of the sensor cannot be assembled on same or built into the sensor, but must be connected to the sensor only after the assembly operation, in order to prevent the cable from rotating during assembly. This requires the use of additional electrical connectors for subsequent connection of the cable to the temperature sensor.